SQLAlchemy¶

This document only include partial usages of SQLAlchemy library for this project.

Please refer to the SQLAlchemy official documentation for detail information.

sqlalchemy.pool.base¶

Base constructs for connection pools.

class Pool(creator, recycle=- 1, echo=None, use_threadlocal=False, logging_name=None, reset_on_return=True, listeners=None, events=None, dialect=None, pre_ping=False, _dispatch=None)¶

Abstract base class for connection pools.

add_listener(listener)¶

Add a PoolListener-like object to this pool.

Deprecated since version 0.7: The _pool.Pool.add_listener() method is deprecated and will be removed in a future release. Please use the _events.PoolEvents listener interface.

listener may be an object that implements some or all of PoolListener, or a dictionary of callables containing implementations of some or all of the named methods in PoolListener.

connect()¶

Return a DBAPI connection from the pool.

The connection is instrumented such that when its close() method is called, the connection will be returned to the pool.

dispose()¶

Dispose of this pool.

This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool.

See also

Pool.recreate()

recreate()¶

Return a new _pool.Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire _pool.Pool and create a new one in its place.

unique_connection()¶

Produce a DBAPI connection that is not referenced by any thread-local context.

This method is equivalent to _pool.Pool.connect() when the :paramref:`_pool.Pool.use_threadlocal` flag is not set to True. When :paramref:`_pool.Pool.use_threadlocal` is True, the _pool.Pool.unique_connection() method provides a means of bypassing the threadlocal context.

sqlalchemy.engine.base¶

class Engine(pool, dialect, url, logging_name=None, echo=None, proxy=None, execution_options=None, hide_parameters=False)¶

Connects a Pool and Dialect together to provide a source of database connectivity and behavior.

An _engine.Engine object is instantiated publicly using the create_engine() function.

See also

/core/engines

connections_toplevel

begin(close_with_result=False)¶

Return a context manager delivering a _engine.Connection with a Transaction established.

E.g.:

with engine.begin() as conn:
    conn.execute("insert into table (x, y, z) values (1, 2, 3)")
    conn.execute("my_special_procedure(5)")

Upon successful operation, the Transaction is committed. If an error is raised, the Transaction is rolled back.

The close_with_result flag is normally False, and indicates that the _engine.Connection will be closed when the operation is complete. When set to True, it indicates the _engine.Connection is in “single use” mode, where the _engine.ResultProxy returned by the first call to _engine.Connection.execute() will close the _engine.Connection when that _engine.ResultProxy has exhausted all result rows.

See also

_engine.Engine.connect() - procure a _engine.Connection from an _engine.Engine.

_engine.Connection.begin() - start a Transaction for a particular _engine.Connection.

connect(**kwargs)¶

Return a new _engine.Connection object.

The _engine.Connection object is a facade that uses a DBAPI connection internally in order to communicate with the database. This connection is procured from the connection-holding _pool.Pool referenced by this _engine.Engine. When the _engine.Connection.close() method of the _engine.Connection object is called, the underlying DBAPI connection is then returned to the connection pool, where it may be used again in a subsequent call to _engine.Engine.connect().

contextual_connect(close_with_result=False, **kwargs)¶

Return a _engine.Connection object which may be part of some ongoing context.

Deprecated since version 1.3: The _engine.Engine.contextual_connect() method is deprecated. This method is an artifact of the threadlocal engine strategy which is also to be deprecated. For explicit connections from an _engine.Engine, use the _engine.Engine.connect() method.

By default, this method does the same thing as _engine.Engine.connect(). Subclasses of _engine.Engine may override this method to provide contextual behavior.

Parameters: close_with_result – When True, the first _engine.ResultProxy created by the _engine.Connection will call the _engine.Connection.close() method of that connection as soon as any pending result rows are exhausted. This is used to supply the “connectionless execution” behavior provided by the _engine.Engine.execute() method.

dispose()¶

Dispose of the connection pool used by this _engine.Engine.

This has the effect of fully closing all currently checked in database connections. Connections that are still checked out will not be closed, however they will no longer be associated with this _engine.Engine, so when they are closed individually, eventually the _pool.Pool which they are associated with will be garbage collected and they will be closed out fully, if not already closed on checkin.

A new connection pool is created immediately after the old one has been disposed. This new pool, like all SQLAlchemy connection pools, does not make any actual connections to the database until one is first requested, so as long as the _engine.Engine isn’t used again, no new connections will be made.

See also

engine_disposal

property driver¶: Driver name of the Dialect in use by this Engine.

execute(statement, *multiparams, **params)¶

Executes the given construct and returns a _engine.ResultProxy.

The arguments are the same as those used by _engine.Connection.execute().

Here, a _engine.Connection is acquired using the _engine.Engine.contextual_connect() method, and the statement executed with that connection. The returned _engine.ResultProxy is flagged such that when the _engine.ResultProxy is exhausted and its underlying cursor is closed, the _engine.Connection created here will also be closed, which allows its associated DBAPI connection resource to be returned to the connection pool.

execution_options(**opt)¶

Return a new _engine.Engine that will provide _engine.Connection objects with the given execution options.

The returned _engine.Engine remains related to the original _engine.Engine in that it shares the same connection pool and other state:

The _pool.Pool used by the new _engine.Engine is the same instance. The _engine.Engine.dispose() method will replace the connection pool instance for the parent engine as well as this one.
Event listeners are “cascaded” - meaning, the new _engine.Engine inherits the events of the parent, and new events can be associated with the new _engine.Engine individually.
The logging configuration and logging_name is copied from the parent _engine.Engine.

The intent of the _engine.Engine.execution_options() method is to implement “sharding” schemes where multiple _engine.Engine objects refer to the same connection pool, but are differentiated by options that would be consumed by a custom event:

primary_engine = create_engine("mysql://")
shard1 = primary_engine.execution_options(shard_id="shard1")
shard2 = primary_engine.execution_options(shard_id="shard2")

Above, the shard1 engine serves as a factory for _engine.Connection objects that will contain the execution option shard_id=shard1, and shard2 will produce _engine.Connection objects that contain the execution option shard_id=shard2.

An event handler can consume the above execution option to perform a schema switch or other operation, given a connection. Below we emit a MySQL use statement to switch databases, at the same time keeping track of which database we’ve established using the _engine.Connection.info dictionary, which gives us a persistent storage space that follows the DBAPI connection:

from sqlalchemy import event
from sqlalchemy.engine import Engine

shards = {"default": "base", shard_1: "db1", "shard_2": "db2"}

@event.listens_for(Engine, "before_cursor_execute")
def _switch_shard(conn, cursor, stmt,
        params, context, executemany):
    shard_id = conn._execution_options.get('shard_id', "default")
    current_shard = conn.info.get("current_shard", None)

    if current_shard != shard_id:
        cursor.execute("use %s" % shards[shard_id])
        conn.info["current_shard"] = shard_id

See also

_engine.Connection.execution_options() - update execution options on a _engine.Connection object.

_engine.Engine.update_execution_options() - update the execution options for a given _engine.Engine in place.

_engine.Engine.get_execution_options()

get_execution_options()¶: Get the non-SQL options which will take effect during execution.

See also

_engine.Engine.execution_options()

has_table(table_name, schema=None)¶: Return True if the given backend has a table of the given name.

See also

metadata_reflection_inspector - detailed schema inspection using the _reflection.Inspector interface.

quoted_name - used to pass quoting information along with a schema identifier.

property name¶: String name of the Dialect in use by this Engine.

raw_connection(_connection=None)¶

Return a “raw” DBAPI connection from the connection pool.

The returned object is a proxied version of the DBAPI connection object used by the underlying driver in use. The object will have all the same behavior as the real DBAPI connection, except that its close() method will result in the connection being returned to the pool, rather than being closed for real.

This method provides direct DBAPI connection access for special situations when the API provided by _engine.Connection is not needed. When a _engine.Connection object is already present, the DBAPI connection is available using the _engine.Connection.connection accessor.

See also

dbapi_connections

run_callable(callable_, *args, **kwargs)¶

Given a callable object or function, execute it, passing a _engine.Connection as the first argument.

The given *args and **kwargs are passed subsequent to the _engine.Connection argument.

This function, along with _engine.Connection.run_callable(), allows a function to be run with a _engine.Connection or _engine.Engine object without the need to know which one is being dealt with.

scalar(statement, *multiparams, **params)¶

Executes and returns the first column of the first row.

The underlying cursor is closed after execution.

schema_for_object = <sqlalchemy.sql.schema._SchemaTranslateMap object>¶

Return the “.schema” attribute for an object.

Used for _schema.Table, Sequence and similar objects, and takes into account the :paramref:`.Connection.execution_options.schema_translate_map` parameter.

New in version 1.1.

See also

schema_translating

table_names(schema=None, connection=None)¶

Return a list of all table names available in the database.

Parameters

schema – Optional, retrieve names from a non-default schema.
connection – Optional, use a specified connection. Default is the contextual_connect for this Engine.

transaction(callable_, *args, **kwargs)¶

Execute the given function within a transaction boundary.

The function is passed a _engine.Connection newly procured from _engine.Engine.contextual_connect() as the first argument, followed by the given *args and **kwargs.

e.g.:

def do_something(conn, x, y):
    conn.execute("some statement", {'x':x, 'y':y})

engine.transaction(do_something, 5, 10)

The operations inside the function are all invoked within the context of a single Transaction. Upon success, the transaction is committed. If an exception is raised, the transaction is rolled back before propagating the exception.

Note

The transaction() method is superseded by the usage of the Python with: statement, which can be used with _engine.Engine.begin():

with engine.begin() as conn:
    conn.execute("some statement", {'x':5, 'y':10})

See also

_engine.Engine.begin() - engine-level transactional context

_engine.Connection.transaction() - connection-level version of _engine.Engine.transaction()

update_execution_options(**opt)¶

Update the default execution_options dictionary of this _engine.Engine.

The given keys/values in **opt are added to the default execution options that will be used for all connections. The initial contents of this dictionary can be sent via the execution_options parameter to _sa.create_engine().

See also

_engine.Connection.execution_options()

_engine.Engine.execution_options()

sqlalchemy.orm¶

Functional constructs for ORM configuration.

See the SQLAlchemy object relational tutorial and mapper configuration documentation for an overview of how this module is used.

class Session(bind=None, autoflush=True, expire_on_commit=True, _enable_transaction_accounting=True, autocommit=False, twophase=False, weak_identity_map=None, binds=None, extension=None, enable_baked_queries=True, info=None, query_cls=None)¶

Manages persistence operations for ORM-mapped objects.

The Session’s usage paradigm is described at /orm/session.

add(instance, _warn=True)¶

Place an object in the Session.

Its state will be persisted to the database on the next flush operation.

Repeated calls to add() will be ignored. The opposite of add() is expunge().

add_all(instances)¶: Add the given collection of instances to this Session.

begin(subtransactions=False, nested=False)¶

Begin a transaction on this Session.

Warning

The Session.begin() method is part of a larger pattern of use with the Session known as autocommit mode. This is essentially a legacy mode of use and is not necessary for new applications. The Session normally handles the work of “begin” transparently, which in turn relies upon the Python DBAPI to transparently “begin” transactions; there is no need to explicitly begin transactions when using modern Session programming patterns. In its default mode of autocommit=False, the Session does all of its work within the context of a transaction, so as soon as you call Session.commit(), the next transaction is implicitly started when the next database operation is invoked. See session_autocommit for further background.

The method will raise an error if this Session is already inside of a transaction, unless :paramref:`~.Session.begin.subtransactions` or :paramref:`~.Session.begin.nested` are specified. A “subtransaction” is essentially a code embedding pattern that does not affect the transactional state of the database connection unless a rollback is emitted, in which case the whole transaction is rolled back. For documentation on subtransactions, please see session_subtransactions.

Parameters

subtransactions – if True, indicates that this begin() can create a “subtransaction”.
nested – if True, begins a SAVEPOINT transaction and is equivalent to calling begin_nested(). For documentation on SAVEPOINT transactions, please see session_begin_nested.

Returns

the SessionTransaction object. Note that SessionTransaction acts as a Python context manager, allowing Session.begin() to be used in a “with” block. See session_autocommit for an example.

See also

session_autocommit

Session.begin_nested()

begin_nested()¶

Begin a “nested” transaction on this Session, e.g. SAVEPOINT.

The target database(s) and associated drivers must support SQL SAVEPOINT for this method to function correctly.

For documentation on SAVEPOINT transactions, please see session_begin_nested.

Returns: the SessionTransaction object. Note that SessionTransaction acts as a context manager, allowing Session.begin_nested() to be used in a “with” block. See session_begin_nested for a usage example.

See also

session_begin_nested

pysqlite_serializable - special workarounds required with the SQLite driver in order for SAVEPOINT to work correctly.

bind_mapper(mapper, bind)¶

Associate a _orm.Mapper or arbitrary Python class with a “bind”, e.g. an _engine.Engine or _engine.Connection.

The given entity is added to a lookup used by the Session.get_bind() method.

Parameters

mapper – a _orm.Mapper object, or an instance of a mapped class, or any Python class that is the base of a set of mapped classes.
bind – an _engine.Engine or _engine.Connection object.

See also

session_partitioning

:paramref:`.Session.binds`

Session.bind_table()

bind_table(table, bind)¶

Associate a _schema.Table with a “bind”, e.g. an _engine.Engine or _engine.Connection.

The given _schema.Table is added to a lookup used by the Session.get_bind() method.

Parameters

table – a _schema.Table object, which is typically the target of an ORM mapping, or is present within a selectable that is mapped.
bind – an _engine.Engine or _engine.Connection object.

See also

session_partitioning

:paramref:`.Session.binds`

Session.bind_mapper()

bulk_insert_mappings(mapper, mappings, return_defaults=False, render_nulls=False)¶

Perform a bulk insert of the given list of mapping dictionaries.

The bulk insert feature allows plain Python dictionaries to be used as the source of simple INSERT operations which can be more easily grouped together into higher performing “executemany” operations. Using dictionaries, there is no “history” or session state management features in use, reducing latency when inserting large numbers of simple rows.

The values within the dictionaries as given are typically passed without modification into Core _expression.Insert() constructs, after organizing the values within them across the tables to which the given mapper is mapped.

New in version 1.0.0.

Warning

The bulk insert feature allows for a lower-latency INSERT of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw INSERT of records.

Please read the list of caveats at bulk_operations_caveats before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters

mapper – a mapped class, or the actual _orm.Mapper object, representing the single kind of object represented within the mapping list.
mappings – a sequence of dictionaries, each one containing the state of the mapped row to be inserted, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary must contain all keys to be populated into all tables.
return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, :paramref:`.Session.bulk_insert_mappings.return_defaults` greatly reduces the performance gains of the method overall. If the rows to be inserted only refer to a single table, then there is no reason this flag should be set as the returned default information is not used.
render_nulls –
When True, a value of None will result in a NULL value being included in the INSERT statement, rather than the column being omitted from the INSERT. This allows all the rows being INSERTed to have the identical set of columns which allows the full set of rows to be batched to the DBAPI. Normally, each column-set that contains a different combination of NULL values than the previous row must omit a different series of columns from the rendered INSERT statement, which means it must be emitted as a separate statement. By passing this flag, the full set of rows are guaranteed to be batchable into one batch; the cost however is that server-side defaults which are invoked by an omitted column will be skipped, so care must be taken to ensure that these are not necessary.

Warning

When this flag is set, server side default SQL values will not be invoked for those columns that are inserted as NULL; the NULL value will be sent explicitly. Care must be taken to ensure that no server-side default functions need to be invoked for the operation as a whole.

New in version 1.1.

See also

bulk_operations

Session.bulk_save_objects()

Session.bulk_update_mappings()

bulk_save_objects(objects, return_defaults=False, update_changed_only=True, preserve_order=True)¶

Perform a bulk save of the given list of objects.

The bulk save feature allows mapped objects to be used as the source of simple INSERT and UPDATE operations which can be more easily grouped together into higher performing “executemany” operations; the extraction of data from the objects is also performed using a lower-latency process that ignores whether or not attributes have actually been modified in the case of UPDATEs, and also ignores SQL expressions.

The objects as given are not added to the session and no additional state is established on them, unless the return_defaults flag is also set, in which case primary key attributes and server-side default values will be populated.

New in version 1.0.0.

Warning

The bulk save feature allows for a lower-latency INSERT/UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw INSERT/UPDATES of records.

Please read the list of caveats at bulk_operations_caveats before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters

objects –
a sequence of mapped object instances. The mapped objects are persisted as is, and are not associated with the Session afterwards.

For each object, whether the object is sent as an INSERT or an UPDATE is dependent on the same rules used by the Session in traditional operation; if the object has the InstanceState.key attribute set, then the object is assumed to be “detached” and will result in an UPDATE. Otherwise, an INSERT is used.

In the case of an UPDATE, statements are grouped based on which attributes have changed, and are thus to be the subject of each SET clause. If update_changed_only is False, then all attributes present within each object are applied to the UPDATE statement, which may help in allowing the statements to be grouped together into a larger executemany(), and will also reduce the overhead of checking history on attributes.
return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, :paramref:`.Session.bulk_save_objects.return_defaults` greatly reduces the performance gains of the method overall.
update_changed_only – when True, UPDATE statements are rendered based on those attributes in each state that have logged changes. When False, all attributes present are rendered into the SET clause with the exception of primary key attributes.
preserve_order –
when True, the order of inserts and updates matches exactly the order in which the objects are given. When False, common types of objects are grouped into inserts and updates, to allow for more batching opportunities.

New in version 1.3.

See also

bulk_operations

Session.bulk_insert_mappings()

Session.bulk_update_mappings()

bulk_update_mappings(mapper, mappings)¶

Perform a bulk update of the given list of mapping dictionaries.

The bulk update feature allows plain Python dictionaries to be used as the source of simple UPDATE operations which can be more easily grouped together into higher performing “executemany” operations. Using dictionaries, there is no “history” or session state management features in use, reducing latency when updating large numbers of simple rows.

New in version 1.0.0.

Warning

The bulk update feature allows for a lower-latency UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw UPDATES of records.

Please read the list of caveats at bulk_operations_caveats before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters

mapper – a mapped class, or the actual _orm.Mapper object, representing the single kind of object represented within the mapping list.
mappings – a sequence of dictionaries, each one containing the state of the mapped row to be updated, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary may contain keys corresponding to all tables. All those keys which are present and are not part of the primary key are applied to the SET clause of the UPDATE statement; the primary key values, which are required, are applied to the WHERE clause.

See also

bulk_operations

Session.bulk_insert_mappings()

Session.bulk_save_objects()

close()¶

Close this Session.

This clears all items and ends any transaction in progress.

If this session were created with autocommit=False, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed.

commit()¶

Flush pending changes and commit the current transaction.

If no transaction is in progress, this method raises an InvalidRequestError.

By default, the Session also expires all database loaded state on all ORM-managed attributes after transaction commit. This so that subsequent operations load the most recent data from the database. This behavior can be disabled using the expire_on_commit=False option to sessionmaker or the Session constructor.

If a subtransaction is in effect (which occurs when begin() is called multiple times), the subtransaction will be closed, and the next call to commit() will operate on the enclosing transaction.

When using the Session in its default mode of autocommit=False, a new transaction will be begun immediately after the commit, but note that the newly begun transaction does not use any connection resources until the first SQL is actually emitted.

See also

session_committing

connection(mapper=None, clause=None, bind=None, close_with_result=False, execution_options=None, **kw)¶

Return a _engine.Connection object corresponding to this Session object’s transactional state.

If this Session is configured with autocommit=False, either the _engine.Connection corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the _engine.Connection returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted).

Alternatively, if this Session is configured with autocommit=True, an ad-hoc _engine.Connection is returned using _engine.Engine.connect() on the underlying _engine.Engine.

Ambiguity in multi-bind or unbound Session objects can be resolved through any of the optional keyword arguments. This ultimately makes usage of the get_bind() method for resolution.

Parameters

bind – Optional _engine.Engine to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over mapper, clause.
mapper – Optional mapper() mapped class, used to identify the appropriate bind. This argument takes precedence over clause.
clause – A _expression.ClauseElement (i.e. _expression.select(), _expression.text(), etc.) which will be used to locate a bind, if a bind cannot otherwise be identified.
close_with_result – Passed to _engine.Engine.connect(), indicating the _engine.Connection should be considered “single use”, automatically closing when the first result set is closed. This flag only has an effect if this Session is configured with autocommit=True and does not already have a transaction in progress.
execution_options –
a dictionary of execution options that will be passed to _engine.Connection.execution_options(), when the connection is first procured only. If the connection is already present within the Session, a warning is emitted and the arguments are ignored.

New in version 0.9.9.

See also

session_transaction_isolation
**kw – Additional keyword arguments are sent to get_bind(), allowing additional arguments to be passed to custom implementations of get_bind().

delete(instance)¶

Mark an instance as deleted.

The database delete operation occurs upon flush().

property deleted¶: The set of all instances marked as ‘deleted’ within this Session

property dirty¶

The set of all persistent instances considered dirty.

E.g.:

some_mapped_object in session.dirty

Instances are considered dirty when they were modified but not deleted.

Note that this ‘dirty’ calculation is ‘optimistic’; most attribute-setting or collection modification operations will mark an instance as ‘dirty’ and place it in this set, even if there is no net change to the attribute’s value. At flush time, the value of each attribute is compared to its previously saved value, and if there’s no net change, no SQL operation will occur (this is a more expensive operation so it’s only done at flush time).

To check if an instance has actionable net changes to its attributes, use the Session.is_modified() method.

enable_relationship_loading(obj)¶

Associate an object with this Session for related object loading.

Warning

enable_relationship_loading() exists to serve special use cases and is not recommended for general use.

Accesses of attributes mapped with _orm.relationship() will attempt to load a value from the database using this Session as the source of connectivity. The values will be loaded based on foreign key and primary key values present on this object - if not present, then those relationships will be unavailable.

The object will be attached to this session, but will not participate in any persistence operations; its state for almost all purposes will remain either “transient” or “detached”, except for the case of relationship loading.

Also note that backrefs will often not work as expected. Altering a relationship-bound attribute on the target object may not fire off a backref event, if the effective value is what was already loaded from a foreign-key-holding value.

The Session.enable_relationship_loading() method is similar to the load_on_pending flag on _orm.relationship(). Unlike that flag, Session.enable_relationship_loading() allows an object to remain transient while still being able to load related items.

To make a transient object associated with a Session via Session.enable_relationship_loading() pending, add it to the Session using Session.add() normally. If the object instead represents an existing identity in the database, it should be merged using Session.merge().

Session.enable_relationship_loading() does not improve behavior when the ORM is used normally - object references should be constructed at the object level, not at the foreign key level, so that they are present in an ordinary way before flush() proceeds. This method is not intended for general use.

See also

:paramref:`_orm.relationship.load_on_pending` - this flag allows per-relationship loading of many-to-ones on items that are pending.

make_transient_to_detached() - allows for an object to be added to a Session without SQL emitted, which then will unexpire attributes on access.

execute(clause, params=None, mapper=None, bind=None, **kw)¶

Execute a SQL expression construct or string statement within the current transaction.

Returns a _engine.ResultProxy representing results of the statement execution, in the same manner as that of an _engine.Engine or _engine.Connection.

E.g.:

result = session.execute(
            user_table.select().where(user_table.c.id == 5)
        )

execute() accepts any executable clause construct, such as _expression.select(), _expression.insert(), _expression.update(), _expression.delete(), and _expression.text(). Plain SQL strings can be passed as well, which in the case of Session.execute() only will be interpreted the same as if it were passed via a _expression.text() construct. That is, the following usage:

result = session.execute(
            "SELECT * FROM user WHERE id=:param",
            {"param":5}
        )

is equivalent to:

from sqlalchemy import text
result = session.execute(
            text("SELECT * FROM user WHERE id=:param"),
            {"param":5}
        )

The second positional argument to Session.execute() is an optional parameter set. Similar to that of _engine.Connection.execute(), whether this is passed as a single dictionary, or a sequence of dictionaries, determines whether the DBAPI cursor’s execute() or executemany() is used to execute the statement. An INSERT construct may be invoked for a single row:

result = session.execute(
    users.insert(), {"id": 7, "name": "somename"})

or for multiple rows:

result = session.execute(users.insert(), [
                        {"id": 7, "name": "somename7"},
                        {"id": 8, "name": "somename8"},
                        {"id": 9, "name": "somename9"}
                    ])

The statement is executed within the current transactional context of this Session. The _engine.Connection which is used to execute the statement can also be acquired directly by calling the Session.connection() method. Both methods use a rule-based resolution scheme in order to determine the _engine.Connection, which in the average case is derived directly from the “bind” of the Session itself, and in other cases can be based on the mapper() and _schema.Table objects passed to the method; see the documentation for Session.get_bind() for a full description of this scheme.

The Session.execute() method does not invoke autoflush.

The _engine.ResultProxy returned by the Session.execute() method is returned with the “close_with_result” flag set to true; the significance of this flag is that if this Session is autocommitting and does not have a transaction-dedicated _engine.Connection available, a temporary _engine.Connection is established for the statement execution, which is closed (meaning, returned to the connection pool) when the _engine.ResultProxy has consumed all available data. This applies only when the Session is configured with autocommit=True and no transaction has been started.

Parameters

clause – An executable statement (i.e. an Executable expression such as _expression.select()) or string SQL statement to be executed.
params – Optional dictionary, or list of dictionaries, containing bound parameter values. If a single dictionary, single-row execution occurs; if a list of dictionaries, an “executemany” will be invoked. The keys in each dictionary must correspond to parameter names present in the statement.
mapper – Optional mapper() or mapped class, used to identify the appropriate bind. This argument takes precedence over clause when locating a bind. See Session.get_bind() for more details.
bind – Optional _engine.Engine to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over mapper and clause when locating a bind.
**kw – Additional keyword arguments are sent to Session.get_bind() to allow extensibility of “bind” schemes.

See also

sqlexpression_toplevel - Tutorial on using Core SQL constructs.

connections_toplevel - Further information on direct statement execution.

_engine.Connection.execute() - core level statement execution method, which is Session.execute() ultimately uses in order to execute the statement.

expire(instance, attribute_names=None)¶

Expire the attributes on an instance.

Marks the attributes of an instance as out of date. When an expired attribute is next accessed, a query will be issued to the Session object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

To expire all objects in the Session simultaneously, use Session.expire_all().

The Session object’s default behavior is to expire all state whenever the Session.rollback() or Session.commit() methods are called, so that new state can be loaded for the new transaction. For this reason, calling Session.expire() only makes sense for the specific case that a non-ORM SQL statement was emitted in the current transaction.

Parameters

instance – The instance to be refreshed.
attribute_names – optional list of string attribute names indicating a subset of attributes to be expired.

See also

session_expire - introductory material

Session.expire()

Session.refresh()

_orm.Query.populate_existing()

expire_all()¶

Expires all persistent instances within this Session.

When any attributes on a persistent instance is next accessed, a query will be issued using the Session object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

To expire individual objects and individual attributes on those objects, use Session.expire().

The Session object’s default behavior is to expire all state whenever the Session.rollback() or Session.commit() methods are called, so that new state can be loaded for the new transaction. For this reason, calling Session.expire_all() should not be needed when autocommit is False, assuming the transaction is isolated.

See also

session_expire - introductory material

Session.expire()

Session.refresh()

_orm.Query.populate_existing()

expunge(instance)¶

Remove the instance from this Session.

This will free all internal references to the instance. Cascading will be applied according to the expunge cascade rule.

expunge_all()¶

Remove all object instances from this Session.

This is equivalent to calling expunge(obj) on all objects in this Session.

flush(objects=None)¶

Flush all the object changes to the database.

Writes out all pending object creations, deletions and modifications to the database as INSERTs, DELETEs, UPDATEs, etc. Operations are automatically ordered by the Session’s unit of work dependency solver.

Database operations will be issued in the current transactional context and do not affect the state of the transaction, unless an error occurs, in which case the entire transaction is rolled back. You may flush() as often as you like within a transaction to move changes from Python to the database’s transaction buffer.

For autocommit Sessions with no active manual transaction, flush() will create a transaction on the fly that surrounds the entire set of operations into the flush.

Parameters

objects –

Optional; restricts the flush operation to operate only on elements that are in the given collection.

This feature is for an extremely narrow set of use cases where particular objects may need to be operated upon before the full flush() occurs. It is not intended for general use.

get_bind(mapper=None, clause=None)¶

Return a “bind” to which this Session is bound.

The “bind” is usually an instance of _engine.Engine, except in the case where the Session has been explicitly bound directly to a _engine.Connection.

For a multiply-bound or unbound Session, the mapper or clause arguments are used to determine the appropriate bind to return.

Note that the “mapper” argument is usually present when Session.get_bind() is called via an ORM operation such as a Session.query(), each individual INSERT/UPDATE/DELETE operation within a Session.flush(), call, etc.

The order of resolution is:

if mapper given and :paramref:`.Session.binds` is present, locate a bind based first on the mapper in use, then on the mapped class in use, then on any base classes that are present in the __mro__ of the mapped class, from more specific superclasses to more general.
if clause given and Session.binds is present, locate a bind based on _schema.Table objects found in the given clause present in Session.binds.
if Session.binds is present, return that.
if clause given, attempt to return a bind linked to the _schema.MetaData ultimately associated with the clause.
if mapper given, attempt to return a bind linked to the _schema.MetaData ultimately associated with the _schema.Table or other selectable to which the mapper is mapped.
No bind can be found, UnboundExecutionError is raised.

Note that the Session.get_bind() method can be overridden on a user-defined subclass of Session to provide any kind of bind resolution scheme. See the example at session_custom_partitioning.

Parameters

mapper – Optional mapper() mapped class or instance of _orm.Mapper. The bind can be derived from a _orm.Mapper first by consulting the “binds” map associated with this Session, and secondly by consulting the _schema.MetaData associated with the _schema.Table to which the _orm.Mapper is mapped for a bind.
clause – A _expression.ClauseElement (i.e. _expression.select(), _expression.text(), etc.). If the mapper argument is not present or could not produce a bind, the given expression construct will be searched for a bound element, typically a _schema.Table associated with bound _schema.MetaData.

See also

session_partitioning

:paramref:`.Session.binds`

Session.bind_mapper()

Session.bind_table()

identity_map = None¶

A mapping of object identities to objects themselves.

Iterating through Session.identity_map.values() provides access to the full set of persistent objects (i.e., those that have row identity) currently in the session.

See also

identity_key() - helper function to produce the keys used in this dictionary.

info¶

A user-modifiable dictionary.

The initial value of this dictionary can be populated using the info argument to the Session constructor or sessionmaker constructor or factory methods. The dictionary here is always local to this Session and can be modified independently of all other Session objects.

New in version 0.9.0.

invalidate()¶

Close this Session, using connection invalidation.

This is a variant of Session.close() that will additionally ensure that the _engine.Connection.invalidate() method will be called on all _engine.Connection objects. This can be called when the database is known to be in a state where the connections are no longer safe to be used.

E.g.:

try:
    sess = Session()
    sess.add(User())
    sess.commit()
except gevent.Timeout:
    sess.invalidate()
    raise
except:
    sess.rollback()
    raise

This clears all items and ends any transaction in progress.

If this session were created with autocommit=False, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed.

New in version 0.9.9.

property is_active¶

True if this Session is in “transaction mode” and is not in “partial rollback” state.

The Session in its default mode of autocommit=False is essentially always in “transaction mode”, in that a SessionTransaction is associated with it as soon as it is instantiated. This SessionTransaction is immediately replaced with a new one as soon as it is ended, due to a rollback, commit, or close operation.

“Transaction mode” does not indicate whether or not actual database connection resources are in use; the SessionTransaction object coordinates among zero or more actual database transactions, and starts out with none, accumulating individual DBAPI connections as different data sources are used within its scope. The best way to track when a particular Session has actually begun to use DBAPI resources is to implement a listener using the SessionEvents.after_begin() method, which will deliver both the Session as well as the target _engine.Connection to a user-defined event listener.

The “partial rollback” state refers to when an “inner” transaction, typically used during a flush, encounters an error and emits a rollback of the DBAPI connection. At this point, the Session is in “partial rollback” and awaits for the user to call Session.rollback(), in order to close out the transaction stack. It is in this “partial rollback” period that the is_active flag returns False. After the call to Session.rollback(), the SessionTransaction is replaced with a new one and is_active returns True again.

When a Session is used in autocommit=True mode, the SessionTransaction is only instantiated within the scope of a flush call, or when Session.begin() is called. So is_active will always be False outside of a flush or Session.begin() block in this mode, and will be True within the Session.begin() block as long as it doesn’t enter “partial rollback” state.

From all the above, it follows that the only purpose to this flag is for application frameworks that wish to detect if a “rollback” is necessary within a generic error handling routine, for Session objects that would otherwise be in “partial rollback” mode. In a typical integration case, this is also not necessary as it is standard practice to emit Session.rollback() unconditionally within the outermost exception catch.

To track the transactional state of a Session fully, use event listeners, primarily the SessionEvents.after_begin(), SessionEvents.after_commit(), SessionEvents.after_rollback() and related events.

is_modified(instance, include_collections=True, passive=None)¶

Return True if the given instance has locally modified attributes.

This method retrieves the history for each instrumented attribute on the instance and performs a comparison of the current value to its previously committed value, if any.

It is in effect a more expensive and accurate version of checking for the given instance in the Session.dirty collection; a full test for each attribute’s net “dirty” status is performed.

E.g.:

return session.is_modified(someobject)

A few caveats to this method apply:

Instances present in the Session.dirty collection may report False when tested with this method. This is because the object may have received change events via attribute mutation, thus placing it in Session.dirty, but ultimately the state is the same as that loaded from the database, resulting in no net change here.
Scalar attributes may not have recorded the previously set value when a new value was applied, if the attribute was not loaded, or was expired, at the time the new value was received - in these cases, the attribute is assumed to have a change, even if there is ultimately no net change against its database value. SQLAlchemy in most cases does not need the “old” value when a set event occurs, so it skips the expense of a SQL call if the old value isn’t present, based on the assumption that an UPDATE of the scalar value is usually needed, and in those few cases where it isn’t, is less expensive on average than issuing a defensive SELECT.

The “old” value is fetched unconditionally upon set only if the attribute container has the active_history flag set to True. This flag is set typically for primary key attributes and scalar object references that are not a simple many-to-one. To set this flag for any arbitrary mapped column, use the active_history argument with column_property().

Parameters

instance – mapped instance to be tested for pending changes.
include_collections – Indicates if multivalued collections should be included in the operation. Setting this to False is a way to detect only local-column based properties (i.e. scalar columns or many-to-one foreign keys) that would result in an UPDATE for this instance upon flush.
passive –
not used

Deprecated since version 0.8: The :paramref:`.Session.is_modified.passive` flag is deprecated and will be removed in a future release. The flag is no longer used and is ignored.

merge(instance, load=True)¶

Copy the state of a given instance into a corresponding instance within this Session.

Session.merge() examines the primary key attributes of the source instance, and attempts to reconcile it with an instance of the same primary key in the session. If not found locally, it attempts to load the object from the database based on primary key, and if none can be located, creates a new instance. The state of each attribute on the source instance is then copied to the target instance. The resulting target instance is then returned by the method; the original source instance is left unmodified, and un-associated with the Session if not already.

This operation cascades to associated instances if the association is mapped with cascade="merge".

See unitofwork_merging for a detailed discussion of merging.

Changed in version 1.1: - Session.merge() will now reconcile pending objects with overlapping primary keys in the same way as persistent. See change_3601 for discussion.

Parameters

instance – Instance to be merged.
load –
Boolean, when False, merge() switches into a “high performance” mode which causes it to forego emitting history events as well as all database access. This flag is used for cases such as transferring graphs of objects into a Session from a second level cache, or to transfer just-loaded objects into the Session owned by a worker thread or process without re-querying the database.

The load=False use case adds the caveat that the given object has to be in a “clean” state, that is, has no pending changes to be flushed - even if the incoming object is detached from any Session. This is so that when the merge operation populates local attributes and cascades to related objects and collections, the values can be “stamped” onto the target object as is, without generating any history or attribute events, and without the need to reconcile the incoming data with any existing related objects or collections that might not be loaded. The resulting objects from load=False are always produced as “clean”, so it is only appropriate that the given objects should be “clean” as well, else this suggests a mis-use of the method.

See also

make_transient_to_detached() - provides for an alternative means of “merging” a single object into the Session

property new¶: The set of all instances marked as ‘new’ within this Session.

property no_autoflush¶

Return a context manager that disables autoflush.

e.g.:

with session.no_autoflush:

    some_object = SomeClass()
    session.add(some_object)
    # won't autoflush
    some_object.related_thing = session.query(SomeRelated).first()

Operations that proceed within the with: block will not be subject to flushes occurring upon query access. This is useful when initializing a series of objects which involve existing database queries, where the uncompleted object should not yet be flushed.

prepare()¶

Prepare the current transaction in progress for two phase commit.

If no transaction is in progress, this method raises an InvalidRequestError.

Only root transactions of two phase sessions can be prepared. If the current transaction is not such, an InvalidRequestError is raised.

prune()¶

Remove unreferenced instances cached in the identity map.

Deprecated since version 0.7: The Session.prune() method is deprecated along with :paramref:`.Session.weak_identity_map`. This method will be removed in a future release.

Note that this method is only meaningful if “weak_identity_map” is set to False. The default weak identity map is self-pruning.

Removes any object in this Session’s identity map that is not referenced in user code, modified, new or scheduled for deletion. Returns the number of objects pruned.

query(*entities, **kwargs)¶: Return a new _query.Query object corresponding to this Session.

refresh(instance, attribute_names=None, with_for_update=None, lockmode=None)¶

Expire and refresh the attributes on the given instance.

A query will be issued to the database and all attributes will be refreshed with their current database value.

Lazy-loaded relational attributes will remain lazily loaded, so that the instance-wide refresh operation will be followed immediately by the lazy load of that attribute.

Eagerly-loaded relational attributes will eagerly load within the single refresh operation.

Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction - usage of refresh() usually only makes sense if non-ORM SQL statement were emitted in the ongoing transaction, or if autocommit mode is turned on.

Parameters

attribute_names – optional. An iterable collection of string attribute names indicating a subset of attributes to be refreshed.
with_for_update –
optional boolean True indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of _query.Query.with_for_update(). Supersedes the :paramref:`.Session.refresh.lockmode` parameter.

New in version 1.2.
lockmode – Passed to the Query as used by with_lockmode(). Superseded by :paramref:`.Session.refresh.with_for_update`.

See also

session_expire - introductory material

Session.expire()

Session.expire_all()

_orm.Query.populate_existing()

rollback()¶

Rollback the current transaction in progress.

If no transaction is in progress, this method is a pass-through.

This method rolls back the current transaction or nested transaction regardless of subtransactions being in effect. All subtransactions up to the first real transaction are closed. Subtransactions occur when begin() is called multiple times.

See also

session_rollback

scalar(clause, params=None, mapper=None, bind=None, **kw)¶: Like execute() but return a scalar result.

transaction = None¶: The current active or inactive SessionTransaction.

Flask¶

Flask library reference